Several types of spacers for flat panel displays, such as field emission displays, are known in the art. A field emission display includes an envelope structure having an evacuated interspace region between two display plates. Electrons travel across the interspace from a cathode plate (also known as a cathode or a back plate), upon which electron emitting structures, such as Spindt tip or carbon nanotubes, are fabricated, on an anode plate (also known as an anode or face plate), which includes deposits of light emitting materials, or “phosphors”. Typically, the pressure within the evacuated interspace region between the cathode and anode is on the order of 10−6 Torr.
The cathode and anode plates are thin in order to provide low display weight. If the display area is small, such as in a 1 inch diagonal display, and a typical sheet of glass having a thickness of 0.04 inch is utilized for the plates, the display will not collapse or bow significantly. However, if a larger display area is desired, the thin plates are not sufficient to withstand the pressure differential in order to prevent collapse of bowing upon evacuation of the interspace region. For example, a screen having a 30 inch diagonal will have several tons of atmospheric pressure exerted upon it. As a result of this tremendous pressure, spacers play an essential role in large area, light weight displays. Spacers are structures placed between the anode and cathode plates for keeping them a constant distance apart. The spacers, in conjunction with the thin, light weight plates, counteract the atmospheric pressure, allowing the display area to be increased with little or no increase in plate thickness.
Several schemes have been proposed for providing spacers. Some of these schemes include the affixing of spacer (structural members such as glass rods) to the inner surface of one of the display plates. In one such prior art scheme, glass rods are affixed to one of the display plates by applying devitrifyng solder glass frit to one end of the rod or post and bonding the frit to the inner surface of one of the display plates. Another known method uses thermocompression bonding to smash one layer of metal into another layer of metal. The bond that is created is strong enough to permit handling and sealing of the device components.
During operation of a flat panel display, as electrons are emitted toward an anode from the electron emitters, some of the electrons will strike the spacers, resulting in secondary electron emission from the spacers. The secondary electron emissions cause the spacers to have a positive charge (more electrons are departing the spacer than are impacting the spacer), thereby attracting (changing the trajectories) more of the primary electrons. These electrons departing the spacer are prevented from striking the intended pixel causing it to be darker (less than the desired number of electrons) and strike the anode area adjacent to the spacer causing an undesired illuminated area typically shaped as a white line, for example.
It has been shown that directing electrons at the spacers when the anode voltage is substantially reduced can neutralize the charge by adding electrons to the spacer. However, spacers in conventional flat panel displays comprise materials that limit the upper voltage on the anode. At higher anode voltages, e.g., above 5,000 volts to 10,000 volts, the spacers become negatively charged and this neutralizing method does not work.
Accordingly, it is desirable to provide a spacer material for flat panel displays having a high anode voltage. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.